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https://issues.apache.org/jira/browse/HBASE-3894?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dave Latham updated HBASE-3894:
-------------------------------

    Attachment: regionserver_rowLock_set_contention.threads.txt

I'm attaching a sample thread dump.

I examined a heap dump as well, and saw about 160K locks in the TreeSet of row 
locks.

> Thread contention over row locks set monitor
> --------------------------------------------
>
>                 Key: HBASE-3894
>                 URL: https://issues.apache.org/jira/browse/HBASE-3894
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.90.2
>            Reporter: Dave Latham
>            Priority: Blocker
>             Fix For: 0.90.4
>
>         Attachments: regionserver_rowLock_set_contention.threads.txt
>
>
> HRegion maintains a set of row locks.  Whenever any thread attempts to lock 
> or release a row it needs to acquire the monitor on that set.  We've been 
> encountering cases with 30 handler threads all contending for that monitor, 
> blocked progress on the region server.  Clients timeout, and retry making it 
> worse, and the region server stops responding to new clients almost entirely.

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